//
// async_udp_echo_server.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2021 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// ref: https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/example/cpp11/echo/async_udp_echo_server.cpp
//

#include <boost/asio.hpp>
#include <cstdlib>
#include <iostream>

using boost::asio::ip::udp;

class server {
public:
    server(boost::asio::io_context& io_context, short port)
        : socket_(io_context, udp::endpoint(udp::v4(), port))
    {
        do_receive();
    }

    void do_receive()
    {
        socket_.async_receive_from(
            boost::asio::buffer(data_, max_length), sender_endpoint_,
            [this](boost::system::error_code ec, std::size_t bytes_recvd) {
                std::cout << "recive call...\n";
                if (!ec && bytes_recvd > 0) {
                    do_send(bytes_recvd);
                } else {
                    do_receive();
                }
            });
    }

    void do_send(std::size_t length)
    {
        socket_.async_send_to(
            boost::asio::buffer(data_, length), sender_endpoint_,
            [this](boost::system::error_code /*ec*/, std::size_t /*bytes_sent*/) {
                do_receive();
            });
    }

private:
    udp::socket socket_;
    udp::endpoint sender_endpoint_;
    enum { max_length = 1024 };
    char data_[max_length];
};

int main(int argc, char* argv[])
{
    try {
        if (argc != 2) {
            std::cerr << "Usage: async_udp_echo_server <port>\n";
            return 1;
        }

        boost::asio::io_context io_context;

        server s(io_context, std::atoi(argv[1]));

        io_context.run();
    } catch (std::exception& e) {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}